Rollout (or Spill Switch?) Tripping on Brand New Boiler?

NewGuy

https://forum.heatinghelp.com/discussion/comment/1814999#Comment_1814999

It's tricky because I'm not sure when the switch is tripping… I was able to turn the boiler back on when it was nicer out on Friday afternoon and Monday morning - above 50 and maybe in the 60s. These were test runs. On Monday it was off all afternoon. When it got colder in the evening (50s and 40s) it wouldn't start.

Tuesday they came to reset the switch and the same thing happened. Test run OK. Off all day. But then it wouldn't start in the evening.

Yesterday the installer reset the switch and started it around 11AM. I turned up the thermostat setting and it ran all day until 8 PM when it reached the thermostat setting. It was about 48 outside at that time. When the temp inside dropped again, the boiler came back on one more time. (This was unique. Most of the day it had been cycling on and off, but last night it turned off then back on one time due to thermostat settings). But by 10:00 PM it had turned off due to thermostat settings and the switch was dead again.

That's a lot to say that I think it struggles when the temp gets to lower 50s and definitely in the 40s.

And the previous boiler…was it operated under conditions where the switch tripped? Not to my knowledge. I didn't know much about spills or rollouts until this week.

JUGHNE

The old boiler, may have had the spill switch or someone may have jumped it out.

pecmsg

now your confusing BTU/h with EDR!

Once you insulate and seal the envelope you change the BTU/h loss. Additionally you’ve changed the size of the radiators in turn that changes the EDR!

Will it work, at this point no one knows!

Jamie Hall

eh? @pecmsg I think you got the wrong thread?

Bob Harper

Wow! Great discussion. I'll yield to the Wet Heads on the EDR/ sizing rabbit trail and stick to the venting.

Yes Ed, spot on with a few thoughts. When you have a 3-story tube that holds about 8.5 lbs of air vertically you have to push this slug of cold dense air up and out to 'prime' the vent and get it going. The hot exhaust gases are not required by law to push all the air out like a piston. When first firing, a central column of hot gases may work its way north while cold dense air around the perimeter continues to slide down the stack. At the same time, there will be Stack Effect in the building meaning negative pressure in the Combustion Appliance Zone (CAZ) pulling against the stack air that you must also overcome. If there are openings at the top of the building, or above the Neutral Pressure Plane, the Stack Effect will be exacerbated. If anyone sleeps with a window open or running an exhaust fan, even worse. Reverse venting, reverse flow, backdraft, etc. all mean it is venting the wrong way. Compare the approximate 105 cubic feet of stack volume with the building. Which would equate to a bigger hot air balloon? It's a tug of war and the house is winning.

The aluminum liner in B-vent sucks heat out of the stack gases. I always use type L vent listed to UL 641. It's not only approved for oil but CAT I gas as well. It has a stainless-steel inner liner that heats slower and doesn't rob heat nearly as badly as aluminum. The stack temps tend to remain higher with L vent over B vent. I would get on the roof and measure the exhaust temp. If you can, measure the exit velocity and Rh%. I'll bet that vent is raining at standby.

A chase is a great idea and Ed's right on several points. Not only should it be as tight as a ducks rear end (no cold air infiltration) but properly weatherized. Notice I didn't say 'insulated'. The chase must be foamed or caulked at the seams all the way. The chase must have suffcient 'R' value. The inner face of the chase MUST be sheathed. You cannot leave insulation, even if unfaced batts of fiberglass or, better Rockwool exposed to the vent pipe. Should it sag against the pipe, it can cause overheating. The 1" clearance to combustibles is an air space. The stated 'R' value of any insulation is valid ONLY if it is sheathed on all sides. You cannot have convection air cooling one face. It's why attic insulation values are a joke. The inner sheathing can be ordinary combustibles. I recommend Thermo-Ply or Thermo-Sheath. It does not have to be type X 'fire code' drywall, cementitious backer board (e.g. Durock) or Superman's cape. Regular drywall meets the requirement but makes for good food for mold. You can take T-ply, crease it in the corners and wrap it around. Secure with roofing nails. The seams get sealed with UL 181 duct mastic or foil tape. The top of the chase will be uninsulated. Have a custom ss chase cover made that overlaps 4" on the sides, cross-broken with a 2" raised collar. Install a storm collar caulked with silicone to the pipe then the rain cap. Limit the exposed pipe to about 12" so plan your chase height above the roof and adjacent structures accordingly. If you do cut vent holes into the base of the chase just understand it may work bassackwards and cool the chase unless to top is completely tight.

What are you doing to manage condensate? I would expect that base to rot out in no time. What is the transition from unlisted single walled connector to the B-vent? Did you use a listed 'draft hood connector? Is is buried in the foundation wall? You cannot bury single walled unlisted pipe in the wall. The entire connector must be fully accessible and replaceable. That long horizontal connector is way under supported and pretty far from the vertical vent. I would have used L vent as a connector.

You can replicate Jughne's draft test better using a smoke puffer. Open flames are notoriously unreliable indicators and not very sensitive. Shine a light across the opening and puff it. You may see it drawing in on one side and spilling on another.

Keep in mind 'draft' is a pressure differential With Respect To the CAZ vs. the stack. You can have a strong draft pressure with little flow and lots of spillage or backdrafting into the CAZ. Flow is a function of removing the local hindrances thereof (Count Rumford's language from 1795). Properly sized connector, no gizmos in the way like vent damper blades, offsets, joints, long low slopes, hard turns, and smooth vs. rough surface, unrestricted discharge (cap). You want a flow rate of about 0.8 meters per second minimum.

A vent damper is not air tight. Having that whopping big draft hood open to it can allow cooler CAZ air to exfiltrate into the stack, thereby cooling it, leading to a flow reversal. Weird local pressure gradients in the building and CAZ can cause spillage off to one side, either favoring or hindering a spill switch. One solution is to block off the draft hood and replace it with a double acting barometric damper. Set the draft to about -0.03 wci. Install a spill switch at the mouth of the gate. If there is a flow reversal, it will spill into the CAZ. A full backdraft will trip the spill switch but a standby flow reversal probably won't either way, you'll have better control of the stack and cool it down with far less room air while maintaining a stead draft pressure and sufficient dilution air to prevent raining in the stack. Yes, the old boiler may have had such bad stack loss at standby combined with a standing pilot it kept the flue warm.

Another consideration is you standby periods. How long between firing cycles? If the building is over-radiated people tend to either open windows to dump heat or set it back to it has longer standby times. An old building such as this is usually an energy hog leaking out the top of the Thermal Envelope. Weatherization will save energy and make the building warmer- possibly too warm causing behavioral changes. It all should synch. Make sure doors to stair wells are closed and the upper envelope tight. Make provision for sufficent MakeUp Air (MUA) as needed. In a big open basement in an old building you probably have sufficient MUA unless the energy raters foamed the perimeter turning it into a Thermos bottle (Dewars flask). You can attach a draft gauge, get it fired up then open a basement door or window and observe any effects. If no change, you probably have sufficient MUA.

The king of all steps, however, is running combustion analysis. That will tell you if the boiler is firing properly and if it is venting properly. I'd put a low level CO monitor on every floor level.

When someone tells me they 'inspected' a vent, I ask if they passed a brush all the way through without obstructions or run a camera all the way. Until you do, you're guessing.

Great discussion and ideas from all.

neilc

house is leaking like a seive thru the attic, and getting some makeup air back down that flue,

seal the attic

MikeL_2

This is a great informative discussion, but I'm a little confused. Is make up air the same as air for combustion?

AJCimino

Wouldn't it be much simpler to just power vent the boiler? Or, not liking that option use a Tjernlund inline fan inducer. https://www.tjernlund.com/draftinducer.htm

Bob Harper

MUA includes combustion air, excess air through the combustion chamber and dilution air through the draft hood or barometric damper at sufficient pressure for proper draft pressure in the stack. The paradox is, how do you suck in sufficient MUA into the CAZ, which requires a negative pressure yet you need a neutral or positive pressure in the CAZ if you don't want to cancel out the draft pressure? You simply make the MUA available to the CAZ for the appliance to draw as needed OR, according to a study from ANSI, provide powered MUA interlocked to the burner control. Passive MUA sucks. The question is, which way? If you cut holes in the wall between the CAZ and the adjoining space to meet code and the adjoining space is negative WRT the CAZ, it will hinder draft pressure- not help.

Bob Harper

Just because someone sells something doesn't make it legal or a good idea. These 'draft inducers' create positive vent pressure. Code requires venting to be listed for positive vent pressure. That eliminates single walled unlisted connector as well as B-vent, L vent or factory chimney. You'd have to get CAT 3 venting that is listed for positive vent pressure AND those stack temps. Most CAT 4 venting I'm aware of cannot handle the stack temps here.

The only way to do it with the venting at hand is a terminal exhaust fan interlocked to the burner where it sucks the exhaust out. A pressure switch proves negative pressure in the stack, which allows the burner to fire.

NewGuy

https://forum.heatinghelp.com/discussion/comment/1815055#Comment_1815055

So then here's my naive question: Is it possible the new smaller boiler doesnt have the same capacity to push the draft up this 3.5 story uninsulated flue the same way the old bigger boiler did? And regarding the new installation, does this (newly added) piece of venting that travels horizontally across from the right side of the boiler to the left before turning left again and going out to the exterior wall make it worse? I've added a photo of the old boiler to compare how that pipe exited before. It was more of a direct line.

AJCimino

So a power venter. Your making this way more complicated then it needs to be. The length of the smoke pipe coming out of the boiler and the length of the "B"vent going up the side of the house is a lot of mass and cold air for a gas boiler to overcome from a cold start up.

NewGuy

https://forum.heatinghelp.com/discussion/comment/1815102#Comment_1815102

That makes sense. Just wondering if this is something I need because of the smaller boiler and/or the additional venting on the new install compared to the old one.

ethicalpaul

Is it possible the new smaller boiler doesnt have the same capacity to push the draft up this 3.5 story uninsulated flue the same way the old bigger boiler did?

you can’t push a draft, just like you can’t push a rope. The draft hood is open on the bottom right where that safety switch is, right gang?

AJCimino

you can’t push a draft, just like you can’t push a rope. The draft hood is open on the bottom right where that safety switch is, right gang?

Power venter solves the problem, or let me set some hair on fire. Open the vent damper. Set to hold open, and install a L4006 aquastat in the boiler drain tapping set to 120 and keep the boiler warm. You'll have a constant draft. I know your using gas, but your not trying to overcome all that cold air that's in the venting system.

NewGuy

https://forum.heatinghelp.com/discussion/comment/1815108#Comment_1815108

Looking at them now… What happens if the damper is always open? Like why does it shut in the first place? And might leaving it open solve the problem on it's own?

AJCimino

Setting it to hold open may do it. You will using inside air to try and create a constant draft, but you have a lot of cold air and cold pipe to overcome. When there is a gas water heater connected to the venting system, you have a constant pilot and a constant draft going up the chimney. You don't have that, so you have to compensate.

SuperTech

I always leave the flue damper open. They are there in an attempt to add a tiny bit of efficiency to the boiler. The frequency of failure that flue dampers have just isn't worth the bit of efficiency they add by lowering the standby loss. It might help the situation. Certainly Bob Harpers recommendations are the best.

I'm not a big fan of power venters either. They are noisy, require additional maintenance and are just another component that can fail on you at the worst time. Using a chimney is the best option.

AJCimino

Bob Harper said:

"The only way to do it with the venting at hand is a terminal exhaust fan interlocked to the burner where it sucks the exhaust out. A pressure switch proves negative pressure in the stack, which allows the burner to fire. "

Didn't he end his comment saying it an obtuse way to use a power venter. That was my suggestion before it was his. Whether you like them or not (and they do add a bit of complexity to the system), it is the way do solve this quickly and efficiently. Everything requires maintenance, and on the whole, they are very reliable.

ChrisJ

I'm just going to throw this out there as an idea.

My boilers drafthood gets by far the hottest when the boiler shuts down and the damper closes. Now mine works well and if anything drafts too good at times so this could very well not apply to this situation.

That said I think someone needs to at a minimum babysit the boiler for a few cycles and see when that switch is getting hot enough to trip. Is it actually happening when it first fires and that flue is nice and cold? If so that shouldn't take long to find out.

Since you're literally playing with fire id recommend a pro investigate and have a good personal CO alarm with him.

Bob Harper

A boiler doesn't have a pre-purge nor a post-purge. Old very high mass oversized boilers had a standing pilot with gas to help warm the flue a little but the standby losses up the stack were not insignificant. It acted as an overdrive continuing to generate draft pressure for awhile, after the burner cycled off. It took longer to cool down so at the next call for heat the mass was already warm so it didn't rob as much heat early in the firing cycle just to warm that puppy up. The early stages of firing result in a lot of heat going to warm the iron and water (in this case, to make steam). This leaves less heat as a stack loss to generate draft pressure. Therefore, it takes a while to get up to cruising altitude. Compare this with a low mass boiler.

We reduce the mass of boilers to save energy

We improve the heat exchangers to save energy transferring more to the water or steam and less up the stack

We install vent dampers to reduce standby losses and save energy

We install better radiator vents so the rads deliver more heat reliably and repeatably, thus reducing calls for heat thus saving energy

We use electronic ignition systems to save energy

We properly size equipment to the building to save energy while the chimney was designed for a big, inefficient hog that worked.

We do everything we can to save energy, but we forgot to save the people. If you're gonna use atmospheric venting, then it all must work together. You've gotta' resign yourself to a certain minimum amount of stack losses to generate the requisite draft pressure under the conditions of use that can be reasonably expected.

Spill switches, vacuum switches, CO alarms, safety pilots and flame rectification are all spiffy. However, anything made by man can and will eventually fail. They are not bulletproof. You must do what you have to do to Safegard the system from the occupants reasonably. You can follow every sizing chart or hire an enginerd to design a system but neither are a guarantee of performance. The proof is in the pudding. To an extent, we always use our customers as guinea pigs because we just don't know 100% if every system will work. There is always an element of trial and error.

Yes, you can install a Suck-O-Matic at the exhaust terminus and pull those fumes out. You can install an interlocked MUA fan that pressurizes the CAZ during each firing cycle. Both have limitations and drawbacks.

We tend to think "draft" (misnomer- you're talking about 'mass flow') as pulling the smoke up- not pushing the cold dense air. Ok, so how does the cold dense air in the stack get out? We introduce a lower pressure into the base of the stack (draft pressure), which results in the mass flow of cool CAZ air into the stack. As this early firing stage progresses, more and more hot gases make their way up the stack, pushing and shoving against the cold air stuck in the chimney trying to reach outdoors. Its a lot like you in a stadium going against the flow of people on the exit ramp. During those initial minutes of firing, as the first flue gases enter the base of the chimney, sometimes, cold air continues to flow down into the CAZ around the perimeter of the stack as the hot gases rise up the center. This is because the outer walls of the chimney/ vent are cool. The larger the chimney the more pronounced this effect. Try venting 200MBH input up a 8" chimney. Not much problem. Try it on a cold 16"x16" terra cotta lined 40ft exterior chimney- it will fight its way up while the cold air around it continues to slide down into the CAZ. It there is a barometric damper or draft hood, they function as a relief port for this cold air spillage. If not, it can actually flood into the combustion chamber causing mayhem. Incomplete combustion, flame impingement, cooling flames and even rollout. Eventually, you've got to create a piston effect of cool CAZ air being drawn up into the stack by the vacuum of lower draft pressure, which displaces the cold air slug above it. Once that slug of cold air has been purged, you're off to the races. This is why you will see fluctuations in draft pressure throughout the firing cycle and why draft regulation (spelled 'barometric damper') is so important.

Trying to cram too much mass up an undersized flue will never work. It won't compress in an open system. If you increase the velocity by high draft, you lose energy up the stack and can cause incomplete combustion problems. You must have balance Daniel-son.

Bob Harper

https://forum.heatinghelp.com/discussion/comment/1815121#Comment_1815121

AJ, I think you missed my point: That inline 'draft inducer' creates positive vent pressure. You're even calling it a 'power venter'. You cannot use positive vent pressure with this type of venting, which is why I suggested putting a fan at the top where the vent is under negative vent pressure. You'd still have to install a double acting barometric damper so you can regulate the draft pressure, whether created by heat or by fan.

If it makes you feel better, yes, you did broach the subject of mechanical venting. You just used an improper reference. Peace.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1814949#Comment_1814949

With the brackets not being spaced out to the surface of the siding they aren't maintaining clarence, the vent appears to be directly touching the siding. The surface of the siding itself is noncombustible other than the paint but it may have a foam insulation in it or parts of the surface underneath may be touching the back side of the siding.